1. Field of the Invention
The present invention relates to a self-supporting conveyor belt in which a portion of the belt travels in a helical path including a number of superimposed belt tiers to form a spiral stack.
2. Description of the Related Art
It is known to use an endless conveyor belt in high volume production operations to provide long dwell times for the transported product as may be required by certain processes such as cooling or freezing. In such operations, a very long conveyor belt can operate in a relatively small space since the belt is moving in an upward or downward spiral path, whereas a straight line operation requires long conveyors and large amounts of plant floor space.
A known conveyor system of this type is disclosed in U.S. Pat. No. 3,348,659 to Roinestad. In this system, the belt is frictionally driven on the inside edge. The belt is supported by rails which may be covered with a plastic material to reduce friction. The vertical space required for the system is determined by the product height and the dimensions of the belt support structure.
Another known conveyor system is described in U.S. Pat. No. 3,938,651 to Alfred et al. Such belt is self-supporting on both edges which results in a simplified construction and a reduced overall height for the system as compared to systems with belt supports under each tier. This system uses a conveyor belt with links on both sides which are formed as spacers whose upper edge portions are arranged to bear against the lower edge portions of the links of the overlying tier of the endless conveyor belt. As discussed therein, the spacer members contact the underside of the links in the overlying belt tier so that the belt is completely self-supporting, i.e., it need not be supported by guide rails, strips, or similar members, unlike the conveyor belt disclosed in U.S. Pat. No. 3,348,659, discussed above.
Some significant problems exist with self-supporting spiral conveyor belts in use today. One such problem is the potential for the stack of belt tiers to tip over when there is no positive means of maintaining alignment. This problem, commonly referred to as "destacking," frequently results in a significant amount of damaged belting. Attempts to solve this problem of guiding the belt tiers include forming the spacer members with special structure for receiving the top edge of the spacer members of an underlying tier to align the two tiers. See, for example, U.S. Pat. No. 4,858,750 in which the lower edge of the spacer has a central groove to receive the top edge of an adjacent spacer, and U.S. Pat. No. 4,875,343 in which the lower edge of a spacer plate includes opposed tabs which form a V-shaped recess to receive the top edge of an adjacent spacer.
The conveyor systems described above require that the spacer of the underlying belt tier be precisely aligned with the spacer in the overlying tier, thus increasing the possibility of destacking. Moreover, the specially formed mating spacer structure results in a fairly complex arrangement which may result in belt hang-up or catching which also increases the probability of destacking.
Another problem encountered in applications of the aforementioned self-supporting conveyor belts is that access through the side plates to treat the product with, e.g. air, liquid nitrogen or CO.sub.2, is limited. Further, visibility, cleanability, and ability to adjust or direct air flow is impaired. While the conveyor belt disclosed in U.S. Pat. No. 3,938,651 shows central apertures in the spacer plates for passage of treating material, in practice such apertures must be relatively small in order to maintain the structural integrity of the plates. In other words, if the aperture is made large enough to allow substantial flow of treating material then the spacer plates will not be able to support the weight of the overlying belt tiers, which weight is substantial for the lowermost tier.
Accordingly, there is a need in the art for a self-supporting helical conveyor belt which is free of the aforementioned problems.